1. Field of the Invention
This invention relates generally to the field of network data services. More particularly, the invention relates to an improved antenna for receiving signals on a wireless device.
2. Description of the Related Art
Antenna systems used in current cell phones and wireless data processing devices are typically comprised of a single straight wire or conducting loop contained within the devices"" casing. FIGS. 1a and 1b illustrate some of the basic principles associated with antenna theory. The electromagnetic signal received by an antenna 110 is comprised of an electric field vector (E) 120 and a magnetic field vector (H) 130. The magnetic field vector 130 is perpendicular to the electric field vector 120. The wave shown in FIG. 1a is said to be xe2x80x9cvertically polarizedxe2x80x9d because the electric field vector is in a vertical orientation. The plane defined by E and H is a plane of energy (measured in, e.g., watts/m2) traveling in the direction of Wave propagation (Z) 150. The transmitter 100 may transmit the wave at various frequencies and using various types of modulation, depending on the particular standards involved (e.g., CDMA, GSM, TDMA, . . . etc).
The antenna 110 configured within the wireless device 105 also transmits and receives an electric field component (E) 121 and a magnetic field component (not shown). For ideal reception, the electric field component 121 of the wireless device""s antenna 110 should have the same vertical orientation as the electric field component 120 of the base station signal when the wireless device is in the dominant user position. By contrast, if the electric field 121 of the antenna is perpendicular to the electric field 120 of the base station wave, as illustrated in FIG. 1b, the antenna will not effectively receive the base station signal. Because of this cross-polarized condition, the wireless device will not effectively receive vertically polarized signals from the base station when the wireless device is in a horizontal orientation.
FIGS. 2a and 2b plot signal strength as a function of the wireless device""s rotation. The plot shown in FIG. 2a is associated with rotation arrow 140 shown in FIG. 1a and the plot shown in FIG. 2b is associated with rotation arrow 142 shown in FIG. 1b. If the wireless device is rotated along its vertical axis as indicated by rotation arrow 140, the vertical component of the antenna""s electric field 121 remains in a vertical orientation and signal reception strength is excellent because the electric field vectors of both the base station and the wireless device are aligned. If, however, the device is rotated as indicated by rotation arrow 142 in the horizontal position illustrated in FIG. 1b, then the device""s ability to capture energy from the incoming vertically polarized signal is greatly degraded because the electric field of the device""s antenna has rotated from a vertical to a horizontal polarization condition.
In sum, present wireless devices are incapable of effectively receiving vertically polarized waves when the wireless device is in a horizontal orientation. Thus, when placed horizontally on a tabletop, the signal strength generally becomes very weak. Adding an additional antenna may strengthen the signal but adds significantly to the cost and complexity of the device.
Moreover, because the antenna 110 is contained within the wireless device 105 the casing must be limited to dielectric materials such as rubber or plastic in the region containing the antenna. In addition, the antenna 110 may consume a significant amount of space within the device 105 which could otherwise be used to make the device more compact and less expensive to manufacture.
Accordingly, what is needed is an antenna system which can effectively transmit and receive a vertically polarized signal when the wireless device is in the vertically oriented dominant user position as well as when the wireless device is placed horizontally on a table. What is also needed is an antenna system which does not consume space within the wireless device or limit the type of material with which the wireless device may be constructed.
An enclosure for a wireless device is described which may be used as the device""s antenna. In one embodiment, the enclosure is designed such that the wireless device is capable of receiving vertically polarized signals in two distinct orthogonal orientations. The antenna is comprised of two charged front and back conducting plates which propagate an omnidirectional vertically polarized electric field used to transmit and receive electromagnetic signals from a first orientation. In addition, in one embodiment, the size of the plates are selected to propagate a second vertically polarized electric field which is used to transmit and receive electromagnetic signals in a second orthogonal orientation.